Duplex communication system



' 23, 1936. E GERHARD 2,045,224

DUPLEX COMMUNICATION SYSTEM u Filed Nov. 7, lssz Jig. 2

Patented .lune 23, 1936 Aiml'reii'r orties 2,045,224 DUPLEX COMMUNICATION sYs'rEM Ernst Gerhard, Berlin, Germany, assigner to N. V. Machinerieenen Apparaten Fabrieken Meaf,

Utrecht, Netherlands f Application November 7, Serial No. 641,682

In Germany November 7, 1931 9 Claims. (Cl. 2501-.-,9l

The present invention relates to wireless duplex or two-way communication with ultra-short waves.

It is well known that a thermionic valve, which is connected in a damping field circuit, isnot only suitable for generating "ultra-short waves but, provided that the working data are differently adjusted, is also capable of receiving ultra-short waves, the ,circuit being perfectly identical in lo both cases. Y

In order to admit of simultaneous transmitting and receiving, according to the present invention, the working voltages, and/especially the plate Voltage, ofthe valve connected in a brake eld circuit are periodically changed by a control voltage whereby during o-ne half-cycle of the control oscillations, the valve operates as a transmitter and during theother half-cycle it functions as a receiver, the control voltage consuming one half of the cycle during transmitting and the other half during receiving. Instead of one working valve, two Working valves may be used and when'this is the case one works as receiver, one as transmitter and the function of the auxiliary voltage is the same as outlined above.

In order to produce the control frequency, an oscillation generator of super-audible or high frequency is preferably .provided in the communicating stations. Both of the stations may be provided with such a generator, or the generator may be present in only one station. In the first case, where a highgfrequency generator is provided in each station for the periodic control'of the ultrashort wave tube, its frequencies Should be' so chosen that between them an audible differential sound is produced. This sound occurs in each of the' stations and can be used to transmit audible signals as will be described in detail below.

If only one of the stations is provided with 40 such a source of contro-I frequency, the alternating control current in the other station can be produced by amplifying the control frequency of the first station which may be detected as the modulation of the ultra-high frequency received from the second station; this amplified frequency serves for the periodic control orswitching over of the ultra-short wave'tube. The modulation frequencies which permit the transmission of signals are preferably superimposed on the alternating Ycontrol current. In each of vthe stations the ultra-high frequency received is `rectified to give the control frequency of the sending station, and when this is rectified the true modulation frequency is obtained.H If each of the stations 5 uses a high frequency generator, the differential tone of which is audible, signals from one station can be transmitted to the other without any modulation of the control frequencies. If the control frequency of the first station is transmitted for instance in Morse code, sound-frequency signs of the same code are received in the other station.

If both stations operate with the same control frequency or if one cf the stations uses an amplified control frequency received from the other l0 station, interference between the local and remote ,control frequencies may be avoided by synchronization of the frequencies and by shifting the` phase lof the local and remote frequencies through l5l Finally,it is of advantage to block the receiveramplifier during the transmitting half-cycle of thejcontrol oscillations, preferably by periodically displacing the rgrid-potentials of one or more amplifying valves in the frequency of the con- 20 trol voltage, or more especially by using the halfcycle 'control oscillations for the ultra-short waves valves simultaneously for blocking the amplifier.

i Fig. 1 shows the relation between the ultra- 35 high frequency energy N and the plate or brakefield electrode potential EB;

Fig. 2 is an exemplary embodiment of the invention; v

Fig, 3 is another exemplary embodiment of 30 the invention wherein vthe switching or commutating oscillations are synchronized with the modulated oscillations received; and Fig.4 shows the time sequence of the receiving and sending periods.

Fig. l shows schematically a characteristic oscillation curve of an ultra-short wave valve arranged in a brake field circuit. It shows the relation between the ultra-high frequency oscillation energy N and the voltage EB of the brakefleld electrode (plate electrode) with a grid voltage of for example 200 volts. The valve operates as a transmitter in the regio-n of EB=7 volts to EB=23 volts whereas with a potential of about EB=4 v. to -8 v. on the brake-field electrode it is adapted to operate as a receiver. Now if Aan alternating voltage is superimposed on -the normal voltage of the brake-field electrode, which amounts to say EBz-'l volts, ultra-high frequency oscillations will be generated in the valve during each negative half-cycle of this alternating voltage. When the plate or brake-field electrode potential EB is varied between the values '7A v. and -15 v., the tube having the characteristic illustrated in Fig. 1, produces ultra-high frequency oscillations and if this brake-'field potential is periodically varied between these or intermediate voltage values the tube periodically genoscillations the valve will function as a receiver.

However, seeing Vthat the range of voltage in which good reception is obtained is not so great as the range of voltage in which the tube can operate as a transmitter, it is of advantage to suppress entirely the positivehalf-,cycla so that during this time the brake-field electrode pos sesses the normal voltage most suitablerfor.` reception, Viz. about -7 volts.

The frequency of the control oscillations lies preferably outside the range of audibility. Otherwise, the control oscillations which .may cause interference during the reception of telephony, may be ltered out by known'ineans.

VVlijig. 2 shows anV example of the invention. The ultra-short wave valve I `is arranged -in Barkhausen-Kurz connection ora brake field circuit. A high positive D. C. voltage -l- Gof say 200 volts is applied to the grid 2. whilst Vthe brakefield Velectrode 3 is impressed with a smallerpositive or negative direct voltage of .say -7 volts which is taken from the battery 4. Insertedv in the circuit between the brake-field electrode 3 and the cathode 5 is the transformer coil 6, which is coupled to the oscillatory circuit I of the high frequency receiver 8. The positive half-cycle of the auxiliary alternating .voltage supplied tothe terminals a and b is blocked by the valve I0.

The alternating currents which have been arnplified and rectified in the high frequency receiver 3`are conducted to the Vtelephone I5. grid 2 and the brake-field electrode 3 are connected through the ultra-high frequency double conductor I2 to the antenna I I which serves both for transmitting and for receiving. The control oscillations areV supplied fromthe binding posts a and bof the oscillation generator I9. For Vthis purpose, these binding posts are connected to the resistance 9 and valve I E)v connectedY in series. The binding. post a of the source of control current is also connected to. the'iilarnent 5 ofthe tube l, and the variable contact of resistance 9 is connected through coupling coil 6 and battery 4 to the plate or brake-field electrode 3.

VThe operation of this arrangement is as follows: VThe grid 2 of the ultra-short Wave tube carries a high positive current. The plate or brake-field electrode is provided with such direct current from the battery 4 that the ultraesh'ort wave tube I can act either asa receiver or transmitter. When alternating currents are impressed onA the binding posts a and b, a rectid current' is caused to new in resistance 9. VThe variable contact of resistance 9, connected tov theplate or brake-field electrode, is maintained at a negative potential with respect to the cathode, andif Athis potential is sunciently negative,v no current will flow through the vacuum tube from the resistance 9. During the positive portion ofthe alternating control current cycle the voltage of the,plate or brake-field electrode 3 therefore refmains substantially constantat or near the po'- tential of the battery 4 and the tube can act as a receiver of ultra-high frequency signals.

Q-'The sending station is provided in 'the same manner with a source of Aalternating current for .periodic control. The ultra-high frequencysig'- nals which are modulated` by the frequency.of the control frequencyare received. byj the antenna I Iv and Vamplified and rectified in the'ultra'- TheV high frequency tube. The control frequency of the sending station is therefore effective in the plate or brake-field electrode circuit and in the coil 6. This control frequency is received by the oscillation circuit 'I and supplied to the amplifier 8. If the control oscillation of the communicatingstation-l -is first modulated by signal or voice frequencies, these frequencies can be rectified or detected at the end of the amplification ...step and made audible in the telephone I 5.

The transmission of low frequency signals from one-'station to the other can be performed very simply ,by modulating the alternating control .ffrequency; current, supplied by the source I9 Which-*iseither.very high or super-audible fre- .quency by the signal or voice frequencies.

".Toavoid disturbances in the receiving circuits ofthe Vunit 8 by the oscillation produced by the control frequency generator I9, the frequency of thegenerator is. made different from that of the sendinglstaton. so that.,little arno energy from the generator I9 is selected by the oscillation circuit/1. 'Ihecontrol.oscillation` of the receiving s tatoncan also beseparated from. theampliiier 8.. by additional filter circuits` connected between theoscillation circuit. land the amplifier 8. If the .high frequency control oscillations of the two Stationsare so chosen that ,anaudible sound occurs from their supereimposition, this sound can be -usedfortransmission ,of signals. The ampli-'fier 8 then receives anhnmodulated high frequency, .that isoscillations from its own control generator,7 and a second unmodulated high frequency fromV `thesending station through the ultra-high frequency tube I. If the control frequency'A of the communication station is now interrupted-by low.` frequency keying of the transmitted Afrequency in accordance .with the Morse co'de,..corre sponding .lowfrequency signals will be received in .the telephone I5.

' ',Eig..`3 shows an. example of .the .invention "in which ,the4 `control oscillationsware synchronized Withthe: lreceived. modulation oscillations. The

circuit .-of ...the ultra-short wave valve I correspends 4.with that. of Eig. .2. The ultra-short 'WavesgeneratedY by the distant communicating station, are so modulated by a. high-frequency control oscillation, as` described above, that ultrashortlwalmesare` only. radiated duringthe time trof a ,halfrcycle of the control oscillation. The modulation oscillations arising in the/coil 6, of Fig.' 3,.'ofl the receiving station and having been produced. by rectifyin'g' the ultra-short waves by tl`1e ulti'ashort 'wave valve I, have somewhat thefsliap'ofjthe heavilydrawn curves in Fig. 4. These .'rrl'dulation'oscillations are passed through the condenser I6'. to'th'ejgrid. of' the 'amplifying valve 'IIgJaiid energize the oscillatory circuit I3, vvhi'clfjs tuned tojthey fundamentalfrequency of tlfeseoscill'ationis, whereupon they iar'e finally further amplified by the high frequency receiver 114, rectied,.and made audible J'in .the telephone .'I5. 'The unrec'tifiedhiglr-frequency oscillations 'of modulation vfrequency arising in the amplier I'djare "also,- led-over 'the conductor --a-b kto the valvei'lp, which only passes the' negativefhalf= .wave Vof these oscillations; the phase relations 'being 'sojadjusted by suitable choice of'th-ecouplingl elen'l'entslin "the amplifier I4, that lthe negative halfacycle just falls -in the periods-t2 '(seel'ig. '4) during-'Which vno reception takes place. 'Ihe` voltage is so set on thepotentiometer i9; that thevalve I- functions as a transmitter dur;i ing-the time-'tzffof the negative Yhalf-cycle, for example `by- 'arranging -'-that= `the characteristic curve in Fig. 1 is impressed by half the amount, that is, in the region from EB=7 v. to -15 V. This gives rise to a brake field electrode current IB, whose course is denoted in Fig. 4 by the dotted curves. A modulator I8 is connected in the conductor a, b which leads from the high frequency amplifier I4 to the resistance 9 and tube I0. By means of this modulator the control frequency which serves for the periodic control of the ultrashort wave tube, supplied through the amplifier lll, can be modulated by voice or signal frequencies.

The locally produced control oscillations which are displaced in phase by 180 with respect to the received modulation oscillations, are prevented from iniluencing the amplifying valve I1 by arranging that the grid potential of this valve is made so intensely negative by the control oscillations during the times tz, that an automatic blocking takes place. This negative blocking voltage can also be tapped off from the potentiometer 9.

If the arrangement according to Fig. 3 is not to be employed at rst as a receiver as described but as a transmitter, that is, as the calling station, the control oscillations are produced initially in the amplifier I 4, for example, by a suiiiciently high degree of back coupling. As soon as communication has been established with the opposite station, so that ultra-short waves are periodically transmitted from the latter also, the back coupling in the amplifier i4 is made looser, so that the control oscillations are no longer generated by self-energization, but by amplification of the received modulation oscillations.

Instead of one single ultra-short wave valve, two of them may be used and during one-half cycle of the control oscillations the first valve acts as a transmitter and during the other halfcycle, the second valve acts as a receiver. In all the cases described it is possible to use one common reflector for the transmitting and receiving valves.

The above arrangement may be used with aglvantage for measuring distance by the method, already known per se, in which a wave group is transmitted and then received by an opposite station whence it is retransmitted. The distance between the stations may be determined from the time difference between the transmitted and returning groups of waves. In the arrangement according to Fig. l for instance, a group of ultrashort waves is transmitted after an accurately ascertainable time, when the valve I has received the incoming wave group.

I claim:

1. An apparatus for duplex wireless signalling with ultra-short waves, comprising a vacuum tub-e having grid, cathode and plate electrodes, means for impressing a positive potential on the grid electrode with respect to the cathode, means for impressing a varying negative potential on said plate electrode, said last means including means to impress on said plate electrode a constant negative potential and means to superimpose on said constant negative potential a variable potential which is at least in part negative, whereby the potential of said plate electrode varies between more and less negative values, the more negative value being more negative than said constant negative potential, means for generating ultra-high frequency oscillations with said vacuum tube when said potential has said more negative value, means for modulating and transmitting said generated oscillations, and

means for receiving signalling energy when said plate electrode potential has said less negative Value.

2. AnV apparatus for duplex wireless signalling with ultra-short waves, comprising a vacuum tube having grid, cathode and plate electrodes, means for impressing a positive potential on the grid electrode with respect to the cathode, means for impressing a varying negative potential on said plate electrode, said last means including means to impress on said plate electrode a constant negative potential, means for generating a periodically pulsating negative potential, and means to superimpose said pulsating negative potential on said constant negative potential, whereby the potential of said plate electrode varies between more and less negative values, the more negative value being more negative than said constant negative potential, means for generating ultra-high frequency oscillations with said vacuum tube when said potential has said more negative value, means for modulating and transmitting said generated oscillations, and means for receiving signalling energy when said plate electrode potential has said less negative value, a source of alternating current, circuits connected thereto, means for amplifying said received signalling energy and impressing a portion of the amplified signalling energy on said circuits for controlling the operation thereof, and means for detecting and reproducing said received signalling energy.

3. An apparatus for duplex wireless communication with ultra-short waves, comprising a vacuum tube in brake-eld-circuit connection which serves both for transmitting and receiving of ultra-short waves, said tube having a brake-eld-electrode, a source of alternating current supply, means for rectifying the alternating current from said source, means controlle-d by said rectified current to produce a pulsating negative potential, means for impressing the pulsating negative potential on the brake-iield-electrode of said tube, whereby the brake-eld-electrode becomes more negative during alternate half periods of the alternating current for causing said tube to function as an oscillatio-n generator during said half periods, and means for receiving signals during the intervals between said half periods.

4. An apparatus for duplex wireless communication with ultra-short waves, comprising a vacuum tube in brake-eld-circuit connection which serves both for transmitting and receiving of ultra-short waves, said tube having a brakefield-electrode, a source of alternating current supply, means for rectifying the alternating current from said source, means controlled by said rectied current to produce a pulsating negative potential, means for impressing the pulsating negative potential on the brake-field-electrode of said tube, whereby the brake-eld-electrode becomes more negative during alternate half periods of the alternating current for causing said tube to function as an oscillation generator during said half periods, means for receiving signals during the intervals between said half periods, and means for amplifying and detecting said received signals.

5. An apparatus for duplex wireless signalling with ultra-short waves, comprising a vacuum tube having grid, cathode and plate electrodes, means for impressing a positive potential on the grid electrode with respect to the cathode, means for impressing a varying negative potential on said plate electrode, said last means including means to impress on said plate electrode a constant negative potential rand means to superimpose on said constant negative potential a potential which varies through a predetermined cycle and which is at least in part negative, whereby the potential of said plate electrode varies between more and less negative values, the more negative value being more negative than said constant negative potential, means for generating oscillations with said vacuum tube throughout substantially half said predetermined cycle when said potential has said more Ynegative value, means for ymodulating and transmitting said generated oscillations and means for receiving signalling energy throughout the remainder of said rcycle when said plate velectrode potentia has said less negative value.

6. An yapparatus for duplex wireless communication with ultra-short waves, comprising a vacuum tube in brake-eld-circuit connectiony which serves both for transmitting and receiving of yultra-short waves, a source of current supply connected to said tube to supply to the brake-eld-electrode oi said tube a direct current yof such value that the tube when in brakeeld-circuit connection c-an receive ultra-short Wave oscillations, a resistance in the brake-fieldelectrode circuit of said tube, a source oi` control frequency, a vacuum tube connected to said source and to said resistance, whereby during one half period of said source of control frequency, said brake-eld-electrode may be so neg- -atively charged that the short wave tube operates as transmitter.

7. An apparatus for duplex wireless signalling with ultra-short waves, comprising a vacnum tube having grid, cathode and plate electrodes, means for impressing a positive potential f on the grid electrode with respect to the cathode, means forimpressing o-n said plate electrode a negative potential which varies at a superaudio frequency,Y said last means including means to impress on said plate electrode a constant negative potential an-d means to superimpose on said constant negative potential a variable potential which is at least in part negative, whereby the potential oi said plate electrode varies between more and less negative values, the more negative value being more negative than said constant negative potential, means for generating ultra-high frequency oscillations with said vacuum tube when said potential has said more negative v-alue, means for modulating and transmitting said generated oscillations, and means for receiving signalling energy when said plate electrode potential has said less negative value.

8. An apparatus for duplex wireless signalling withultra-short waves, comprising a vacuum tube having grid, cathode and plate electrodes, means for impressing a positive potential on thegrid electrode with respect to the cathode, means for impressing o-n said plate electrode f a negative potential which varies at a superraudioy frequency, said last means including means to impress on said plate electrode a constant negative potential and means to superimpose on said constant negative potential a potential which varies through a predetermined cycle and which is at least in part negative, whereby the Vpotential of said plate electrode varies between more and less negative values, the more negative value being more negative than sai-d constant negative potential, means for generating oscillations ywith said vacuum tube throughout substantially half said predetermined cycle when said potential has said more negative value, means for modulating and transmitting said generated oscillations and means forfreceiving signalling energy throughout the remainder of said cycle when said plate electro-de potential has said less negative value.

f 9. An apparatus for duplex wireless communication with ultra-short Waves, comprising a vacuum tube in brake-ield-circuit Vconnection which serves both for transmitting and receiving of ultra-short waves, said vacuum tube having a brake-iield-electrode, a source of super-audio frequency Y alternating current supply circuits connected thereto, means for rectifyingv the alternating current from'said source, means controlled by sai-d rectified current to produce a pulsating negative potential, means for impressing the pulsating negative potential on the brake-eld-electrode of said tub-e, whereby the brake-eld-electrode becomes more negative during alternate half periods of the alternating current for causing said tube to function as an oscillation generator during said half periods, means for receiving signals during the intervals between said half periods, means for amplifying said received sign-als, means for impressing a portion of said received signals on' said circuits for controlling the operation thereof, and means for detecting and reproducing said received signals.

ERNST GERHARD. 

